Syndrome produced by lesions of the amygdala in monkeys (Macaca mulatta)

Behavioral effects of subtotal amygdaloid lesions were investigated in an attempt to dissociate some of the abnormalities seen after total amygdalectomy. Twelve monkeys received bilateral stereotaxic lesions centered in the basolateral amygdala, lateral amygdala, dorsal amygdala, or the temporal white matter lying adjacent to the lateral amygdala. These monkeys were compared with others with control operations. The control monkeys then received total amygdaloid lesions (AMX). The AMX monkeys exhibited the typical amygdaloid syndrome of hypoemotionality, meat eating, coprophagia, and excessive exploration. In contrast, the monkeys with subtotal amygdaloid lesions would not eat meat or feces, though they were more willing than control monkeys to investigate inanimate objects. Although minor changes in affect were observed, the extreme emotional changes seen after total amygdalectomy were found only in the monkey with the largest subtotal lesion. Only those animals that were hypoemotional showed a deficit in learning successive reversals of an object discrimination. This close association suggests that both the hypoemotionality and the successive reversal deficit arise from the same underlying dysfunction.